Yih-Huei Wan

Experience From Wind Integration in Some High Penetration Areas

The amount of wind power in the world is increasing quickly. The background for this development is improved technology, decreased costs for the units, and increased concern regarding environmental problems of competing technologies such as fossil fuels. The amount of wind power is not spread equally over the world, so in some areas, there is comparatively a high concentration. The aims of this paper are to overview some of these areas, and briefly describe consequences of the increase in wind power. The aim is also to try to draw some generic conclusions, in order to get some estimation about what will happen when the amount of wind power increases for other regions where wind power penetration is expected to reach high values in future

Output Power Correlation Between Adjacent Wind Power Plants

The National Renewable Energy Laboratory (NREL) started a project in 2000 to record long-term, high-frequency (1-Hz) wind power data from large commercial wind power plants in the Midwestern United States. Outputs from about 330 MW of installed wind generating capacity from wind power plants in Lake Benton, MN, and Storm Lake, Iowa, are being recorded. Analysis of the collected data shows that although very short-term wind power fluctuations are stochastic, the persistent nature of wind and the large number of turbines in a wind power plant tend to limit the magnitude of fluctuations and rate of change in wind power production. Analyses of power data confirms that spatial separation of turbines greatly reduces variations in their combined wind power output when compared to the output of a single wind power plant. Data show that high-frequency variations of wind power from two wind power plants 200 km apart are independent of each other, but low-frequency power changes can be highly correlated. This fact suggests that time-synchronized power data and meteorological data can aid in the development of statistical models for wind power forecasting.

Assessment of Simulated Wind Data Requirements for Wind Integration Studies

Wind integration studies are now routinely undertaken by utilities and system operators to investigate the operational impacts of the variability and uncertainty of wind power on the grid. There are widely adopted techniques and assumptions that are used to model the wind data used in these studies. As wind penetration levels increase, some of the assumptions and methodologies are no longer valid and new methodologies have been devised. Based on involvement in conducting studies, reviewing studies, and/or developing datasets for studies in the Western Interconnect, the Eastern Interconnect, Hawaii, and other regions, the authors report on the evolution of techniques to better model the wind power output for cases with high penetrations of wind energy.

Operational Analysis and Methods for Wind Integration Studies

Wind integration studies are increasingly important tools to estimate the impacts that the addition of large amounts of variable and uncertain generation will have on the electricity grid. As the number of these studies has increased in recent years, the sophistication of the methods and assumptions utilized has also increased. These methods have had to evolve with increasing penetration rates and to study changing research questions. In this work, the authors report on the state of the art in this area and make suggestions for improving the methods and assumptions used for cases with high levels of wind power.

A Study of a Wind Farm Power System

A wind power system differs from a conventional power system. In a conventional power plant, the operator can control the plant’s output. The output of a wind farm cannot be controlled because the output fluctuates with the wind. In this study, we investigated only the fixed-frequency induction generator, often used with wind turbines. We adopted the worst-case scenario and conducted a per-phase, per-turbine analysis. Our analysis showed a strong interaction among the wind farm, the utility grid, and the individual generator. In this paper, we investigate the power-system interaction resulting from power variations at wind farms using steady-state analysis. We use the characteristic of a real windsite on a known weak grid. We present different types of capacitor compensations and use phasor diagrams to illustrate the characteristics of these compensations. The purpose of our study is to provide wind farm developers with somc insights on wind farm power systems.Copyright

Angle Instability Detection in Power Systems With High-Wind Penetration Using Synchrophasor Measurements

The alternating current machines in a power system have the ability to remain synchronized following a severe disturbance such as loss of generations, line switching, or fault. This is described as power system transient stability. During system transients, the machines will accelerate or decelerate because of the mismatch between electrical torque and mechanical torque. Their power angles will travel and finally settle down to a new equilibrium, if the system has enough stored energy to absorb the disturbance, and rest the system at another steady state. In case of system instability, some machines will have aperiodic angular separation from the rest of the system and finally lose synchronization. Therefore, the power system transient stability is also called angle stability. The total system inertia is an essential force to rest the system transient. The inertias stored in all rotating masses that are connected to a power system, such as synchronous generators and induction motors, typically respond to disturbances voluntarily, without any control actions; however, several types of renewable generation, particularly those with power electronic interfaces, have an inertial response governed by a control function. To ensure bulk power system stability, there is a need to estimate the equivalent inertia available from a renewable generation plant. An equivalent voluntary inertia constant analogous to that of conventional rotating machines can be used to provide a readily understandable metric, such as the angle instabilities detections, because one of the most difficult obstacles for angle instability detection is the knowledge of the real-time generator inertias. This paper explores a method that utilizes synchrophasor measurements to estimate the equivalent inertia of a power source such as synchronous generators or wind turbine generators. This paper also investigates the angle instability detection method for a system with high wind power penetration using the synchrophasor measurements.

Output Power Correlation Between Nearby Wind Power Plants

The National Renewable Energy Laboratory (NREL) started a project in 2000 to record long-term, high-frequency (1-Hz) wind power output data from large commercial wind power plants. Outputs from about 330 MW of wind generating capacity from wind power plants in Buffalo Ridge, Minnesota, and Storm Lake, Iowa, are being recorded. Analysis of the collected data shows that although very short-term wind power fluctuations are stochastic, the persistent nature of wind and the large number of turbines in a wind power plant tend to limit the magnitudes and rates of changes in the levels of wind power. Analyses of power data confirm that spatial separation greatly reduces variations in the combined wind power output relative to output from a single wind power plant. Data show that high frequency variations of wind power from two wind power plants 200 km apart are independent of each other, but low frequency power changes can be highly correlated. This fact suggests that time-synchronized power data and meteorological data can aid in the development of statistical models for wind power forecasting.© 2003 ASME